Snowmobile construction

ABSTRACT

A snowmobile design, including a modular front suspension system and a stabilizer assembly, a lightweight frame structure and a drive train that reduces the center of gravity of the snowmobile. The modular front suspension system for a snowmobile that is substantially self-contained and self-supporting. The present modular front suspension system is assembled around a primary support structure, such as an extrusion or other structural member. The primary support structure can be easily attached to, or detached from, the snowmobile frame. The modularity of the present suspension system decreases assembly costs. A stabilizer assembly extends through the center opening and is mechanically coupled to the ski spindle housings.  
     The chassis for a snowmobile includes a plurality of front structural members defining a motor compartment. A pair of independent, rear structural members are rigidly connected to the front structural members and extend rearwardly from the motor compartment on opposite sides of an endless belt channel. A protective shell extends between the pair of rear structural members and over the endless belt channel. The protective shell comprises a light-weight, resin based material that transfers substantially no loads between the pair of rear structural members. The snowmobile chassis further includes a rear suspension system extending between the pair of rear structural members. The rear suspension system transfers substantially all loads between the pair of rear structural members.

[0001] The present application claims the benefit of prior filed U.S.provisional application No. 60/114,330 entitled Modular Front SuspensionSystem and Stabilizer Assembly for a Snowmobile, filed Dec. 31, 1998,and U.S. provisional application No. 60/130,000 entitled SnowmobileConstruction, filed Apr. 19, 1999.

FIELD OF THE INVENTION

[0002] This invention is directed to various innovations in snowmobiledesign, including a modular front suspension system and a stabilizerassembly, a lightweight frame structure and a drive train that reducesthe center of gravity of the snowmobile.

BACKGROUND OF THE INVENTION

[0003] Snowmobile design has incrementally moved towards more powerfulmotors, with a resulting increase in the weight of the machines due tothe larger motor and corresponding support structure. Frequently,increased weight results in a higher center of gravity of thesnowmobile. Increased weight and increased center of gravity can have adetrimental affect on the ride quality and handling characteristics ofthe snowmobile.

[0004] Handling, cornering and ride quality are largely dependent uponthe front suspension system of the snowmobile. It is common practice tosuspend the skis of a snowmobile independently by means of respectivestrut type suspensions. It is desirable to provide some form ofstabilizer or sway bar arrangement interconnecting the front skis toreduce the amount of leaning that occurs during cornering of thesnowmobile. Due to the rough and sometimes uncertain terrain over whichsnowmobiles are ridden, it is desirable that the stabilizer arrangementbe positioned so that it will be protected if unexpected objects areencountered, such as disclosed in U.S. Pat. No. 4.690,234 (Takada).

[0005] U.S. Pat. No. 4.489,954 discloses an anti-roll mechanism thatincludes a torsion bar supported by the body that is connected to theskis for torsion loading upon independent movement of the skis relativeto the body. The connection between each of the skis and the torsion baris such that the torsion bar is loaded by the pivotal movement of theskis about their steering axes for providing a self-centering force onthe skis.

[0006] U.S. Pat. No. 4,671,521 (Talbot, et al) discloses a snowmobileski suspension including upper and lower transverse suspension armsvertically spaced and each having an outboard end articulated to a skispindle and an inboard end articulated to a fixed mounting on the frameof the snowmobile. The upper and lower transverse suspension arms definea parallelogram linkage for guiding the spindle to move generallyvertically with respect to the snowmobile.

[0007] U.S. Pat. No. 5,029,664 (Zuwalski) discloses a suspension systemwith a geometry that includes upper and lower suspension linkages ofpredetermined lengths in cooperation with a spindle of a predeterminedlength for eliminating lateral movement of the skis during suspensiontravel. The respective linkages and spindles are interconnected by balljoints at predetermined locations in such a manner that duringdeflection of the suspension system, a ski attached to the lower end ofthe spindle moves substantially in a line parallel to a vertical planewhich contains the longitudinal axis of the snowmobile.

[0008] What is needed is a snowmobile design that provides a highpower-to-weigh ratio while maintaining optimum handling characteristicsand ride quality.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention is directed to various innovations insnowmobile design. In one embodiment, the snowmobile includes a modularfront suspension system and a stabilizer assembly. In anotherembodiment, the frame structure includes a lightweight frame structure.In yet another embodiment, the snowmobile includes a drive train thatreduces the center of gravity. Finally, all of these features arecombined on a single snowmobile.

[0010] The present invention is directed to a modular front suspensionsystem for a snowmobile that is substantially self-contained andself-supporting. The present modular front suspension system isassembled around a primary support structure, such as an extrusion orother structural member. The primary support structure can be easilyattached to, or detached from, the snowmobile frame. The modularity ofthe present suspension system decreases assembly costs.

[0011] The front suspension system of a snowmobile is typicallyassembled directly to the frame of the snowmobile. The present modularfront suspension system can be assembled independently of the snowmobileand conveniently transported or stored for later use. Theself-contained, self-supporting nature of the present suspension systemallows for lower cost assembly, machine handling and automated testing.

[0012] Repairs on conventional snowmobile suspension systems are oftenaccomplished by replacing individual components. End-users, however,typically lack the proper equipment to determine whether the frontsuspension system is operating properly. The present front suspensionsystem can be easily removed by the user and returned to themanufacturer for factory repair. A temporary or permanent replacementsuspension systems can also be sent to the customer for easyinstallation.

[0013] Additionally, a standardized primary support structure can beutilized so that a variety of suspension systems with different featurescan be easily substituted on the snowmobile by the manufacture, thedealer or the end-user. Since the front suspension system is lessexpensive than the entire snowmobile, the manufacturer/dealer can offera variety of options with lower inventory costs. The end-user may alsopurchase multiple front suspension systems for a single snowmobile. Forexample, the end-user may have one front suspension system for racingand another for touring.

[0014] In one embodiment, the modular front suspension system includes aprimary support structure having first and second ends, a center openingand at least one mounting surface attachable to the chassis. A pair ofupper control arms are pivotally connected to the first and second endsof the primary support structure at upper control arm axes,respectively. A pair of lower control arms are pivotally connected tothe first and second ends of the primary support structure at lowercontrol arm axes, respectively. A pair of ski spindle housings arepivotally connected to distal ends of the upper and lower control arms,respectively. The ski spindle housings are connectable to the steerableskis. A stabilizer assembly is mechanically coupled to the ski spindlehousings. In one embodiment, the stabilizer assembly extends through thecenter opening and is mechanically coupled to the ski spindle housings.

[0015] In another embodiment, the modular front suspension systemincludes a primary support structure having first and second ends, acenter opening and at least one mounting surface attachable to thechassis. A pair of upper control arms are pivotally connected to thefirst and second ends of the primary support structure at upper controlarm axes, respectively. A pair of lower control arms are pivotallyconnected to the first and second ends of the primary support structureat lower control arm axes, respectively. A pair of ski spindle housingsare pivotally connected to distal ends of the upper and lower controlarms, respectively. The ski spindle housings are connectable to thesteerable skis. A pair of shock mounts are pivotally attached to one ofthe upper control arm or primary support structure, respectively. A pairof shock absorber are attached to the shock mounts and the spindlehousings, respectively.

[0016] The present invention is also directed to a stabilizer assemblyfor use in a front suspension system on a snowmobile. The presentstabilizer assembly may be used with or without the present modularfront suspension system.

[0017] To provide flat cornering on smooth terrain, the front suspensionsystem initially provides stiff resistance to ski displacement. In theevent that rough terrain is encountered, subsequent ski displacement ispreferably less stiff. That is, the force per unit displacementdecreases with greater displacement. For example, the front suspensionsystem provides stiff resistance to ski displacement during high-speedturns. If bumps are encountered during the turn, the front stabilizersystem provides less resistance to ski displacement as compared to itsinitial movement. In one embodiment, the force per unit displacementcurve is a step function, with greater force per unit displacementrequired during initial displacement and less additional force per unitdisplacement for subsequent displacement.

[0018] In one embodiment, the present stabilizer system includes firstand second stabilizer brackets attached to the control arms,respectively. A rocker arm having first and second ends is pivotallymounted to the snowmobile. A first stabilizer member assembly ispivotally connected to the first stabilizer bracket and the first end ofthe rocker arm. A second stabilizer member assembly is pivotallyconnected to the second stabilizer bracket and the second end of therocker arm. The stabilizer system transfers load from one side of thesnowmobile to another. That is, spring force from one side of thesnowmobile is transferred to the side experiencing he greatest skidisplacement. In one embodiment, the actual spring rate on thestabilizer member assemblies can be different from ski to ski.

[0019] In one embodiment, the stabilizer member assembly includes anextendable rod assembly having a maximum extension and a spring capfixed thereto. A sleeve is slidably engaged with the extendable rodassembly adjacent to the first stabilizer bracket. A spring is arrangedaround the extendable rod assembly and interposed between the spring capand the sleeve. In one embodiment, an adjustment mechanism is providedfor sliding the sleeve along the extendable rod assembly to apply a biasof the spring. The extendable rod assembly is typically a telescopingstructure. The stabilizer member assemblies are typically in a fullyextended or topped-out configuration in a level or horizontal restingstate.

[0020] The stabilizer member assemblies can be configured to provide apreload in the horizontal resting state such that initial upwarddisplacement of one of the skis is resisted by a first force, andsubsequent upward displacement of that ski is resisted by the additionof a second force proportionally less than the first force. In anotherembodiment, the first stabilizer member assembly is a double-actingspring assembly and the second stabilizer members assembly comprises arigid shaft.

[0021] The present modular front suspension system and the presentstabilizer assembly have application in other vehicles, such asautomobiles, trucks and all-terrain vehicles.

[0022] The present invention is also directed to a chassis for asnowmobile having an endless belt drive system. The chassis includes aplurality of front structural members defining a motor compartment.Front suspension system mounting locations are positioned on distal endsof two or more of the front structural members. A pair of independent,rear structural members are rigidly connected to the front structuralmembers and extend rearwardly from the motor compartment on oppositesides of an endless belt channel. A protective shell extends between thepair of rear structural members and over the endless belt channel. Inone embodiment, the protective shell comprises a lightweight, resinbased material that transfers substantially no loads between the pair ofrear structural members. The snowmobile chassis further includes a rearsuspension system extending between the pair of rear structural members.The rear suspension system transfers substantially all loads between thepair of rear structural members.

[0023] In one embodiment, the snowmobile chassis includes a motorlocated in the motor compartment. The motor has at least one carburetorpositioned on a first side of the motor adjacent to the front suspensionsystem mounting locations and an exhaust port positioned on a secondside of the motor.

[0024] The present invention is also directed to a snowmobile chassishaving a motor compartment and an endless belt channel. A motor islocated in the motor compartment. The motor has at least one carburetorpositioned on a first side of the motor adjacent to a front suspensionsystem and an exhaust port positioned on a second side of the motor. Themotor has a drive clutch. A driven pulley is located on a gearbox thatis located adjacent to the endless belt channel. An endless belt driveshaft is located in the endless belt channel and mechanically coupleddirectly to the gearbox. A drive belt mechanically couples the driveclutch to the driven pulley. A torque arm connects the driven pulley tothe snowmobile chassis.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0025]FIG. 1 is a perspective view of a modular suspension system inaccordance with the present invention.

[0026]FIG. 2 is a front view of a portion of the suspension system ofFIG. 1.

[0027]FIG. 3 is a perspective view of a portion of a front suspensionsystem in accordance with the present invention with the supportstructure removed.

[0028]FIG. 4 is an exploded view of a stabilizer member assembly inaccordance with the present invention.

[0029]FIG. 4A illustrates an alternate stabilizer member assembly inaccordance with the present invention.

[0030]FIG. 5 is a perspective view of a stabilizer system in accordancewith the present invention.

[0031]FIG. 6 is a top view of the stabilizer system of FIG. 5

[0032]FIG. 7 is a rear view of the stabilizer system of FIG. 5.

[0033]FIG. 8 is a perspective view of the present front suspensionassembly mounted to a snowmobile frame.

[0034]FIG. 9 is a side view of a primary support structure in accordancewith the present invention mounted to a snowmobile chassis.

[0035]FIG. 10 is a side perspective view of a snowmobile chassis inaccordance with the present invention.

[0036]FIG. 11 is a front perspective view of a snowmobile chassis ofFIG. 10.

[0037]FIG. 12 is a rear perspective view of a snowmobile chassis of FIG.10.

[0038]FIG. 13 is a side view of a snowmobile motor and drive train inaccordance with the present invention.

[0039]FIG. 14 is a top view of a snowmobile motor and drive train ofFIG. 13.

[0040]FIG. 15 is a perspective view of a torque arm in accordance withthe present invention.

[0041]FIG. 16 is an exploded view of a snowmobile gearbox in accordancewith with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0042] FIGS. 1-2 illustrate various aspects of a modular frontsuspension system 20 in accordance with the present invention. Thevarious components of the modular front suspension system 20 are builtaround and attached to a primary support structure 22. In theillustrated embodiments, the primary support structure 22 comprises ahollow metal extrusion, preferably constructed from an aluminum alloy.In an alternate embodiment, the primary support structure 22 may be anI-beam, a solid member, a welded member, a cast member, a hollow membercontaining reinforcing webs, or a variety of other structures. Steeringbrackets 24 a, 24 b are attached to the primary support structure 22 forreceiving a steering linkage mechanism (not shown).

[0043] Various mounting holes 23 are located on the primary supportstructure 22 for attachment to the snowmobile frame 200 (see FIGS. 8 and9). The primary support structure 22 defines a center opening 72.Stabilizer assembly 74 is located in the center opening 72 (see alsoFIG. 9). Since the modular front suspension assembly is generallysymmetrical, corresponding components are generally referred to hereinwith the suffix “a” or “b”, while these components may also be referredto generically without the suffix.

[0044] The modular front suspension system 20 includes upper controlarms 28 a, 28 b pivotally mounted to the primary support structure 22 atupper control arm axes 30 a, 30 b. Lower control arms 32 a, 32 b arepivotally mounted to the primary support structure 22 at lower controlarm axes 34 a, 34 b. In the illustrated embodiment, the upper controlarm axes 30 a, 30 b are located above the lower control arm axes 34 a,34 b, with respect to the front suspension system 20 being mounted to asnowmobile frame (see FIG. 8). Distal ends of the upper and lowercontrol arms 28 a, 32 a, 28 b, 32 b are pivotally attached to spindlehousings 36 a, 36 b at axes 40 a, 42 a, 40 b, 42 b, respectively. Thespindle housings 36 a, 36 b includes openings 38 a, 38 b for receiving aski spindle and ski (not shown).

[0045] Shock mounts 50 a, 50 b are pivotally attached to either theprimary support structure 22 or the upper control arms axes 30 a, 30 b.In the illustrated embodiment, the shock mounts 50 a, 50 b are mountedto the primary support structure 22 along the upper control arm axes 30a, 30 b. The shock mounts 50 a, 50 b includes a pair of holes definingaxes 54 a, 54 b for receiving a shock absorber assembly 70 (see alsoFIG. 8).

[0046] Lower shock mounts 56 a, 56 b are rigidly attached to therespective spindle housings 36 a, 36 b. In an alternate embodiment, thelower shock mounts 56 a, 56 b can be attached to the lower control arms32 a, 32 b, respectively. The upper control arms 28 a, 28 b includeshock absorber openings 60 a, 60 b. The lower control arms 32 a, 32 binclude shock absorber openings 62 a, 62 b. The shock absorber openings60, 62 permit a shock absorbers 70 a, 70 b (see FIGS. 3 and 8) to bepivotally mounted to the axes 54 a, 54 b of the shock mounts 50 a, 50 band axes 58 a, 58 b of the lower shock mounts 56 a, 56 b. As best seenin FIG. 2, lower portion of the shock mounts 50 a, 50 b are pivotallyconnected to the lower control arms 32 a, 32 b by links 69 a, 69 b. Inanother embodiment, the shock mounts 50 a, 50 b may be attached directlyto the primary Support structure 22 or the vehicle chassis 240.

[0047] The stabilizer assembly 74 includes a rocker arm 76 pivotallymounted within the primary support structure 22 to rotate around an axis78. First and second ends 80, 82 of the rocker arm 76 are pivotallyattached to respective stabilizer member assemblies 84 a, 84 b. Thestabilizer member assemblies 84 a, 84 b are pivotally attached to thelower control arms 32 a, 32 b by a pair of stabilizer brackets 88 a, 88b (see FIG. 5). In an alternate embodiment, the stabilizer brackets 88a, 88 b are pivotally attached to the upper control arms 28 a, 28 b orthe shock mounts 50 a, 50 b.

[0048]FIG. 3 is a perspective view of one side of the present modularfront suspension system 20 and a portion of the stabilizer assembly 74with the primary support structure 22 removed. Shock absorber 70 aextends through the opening 60 a, 62 ain the upper and lower controlarms 28 a, 32 a. In the illustrated embodiment, the shock absorberassembly 70 a includes a shock absorber 71 a surrounded by a spring 73a, although other shock absorber or spring assemblies are possible.

[0049]FIG. 4 is an exploded view of the stabilizer member assemblies 84a, 84 b in accordance with the present invention. Control arm mountingportion 90 includes a slot 92 for receiving a sliding nut 94. Rod 96engages with the sliding nut 94. The sliding nut 94 permits the rod 96to telescope or extend relative to the control arm-mounting portion 90along the full length of the slot 92. The stabilizer member assemblies84 a, 84 b top-out or bottom-out when the sliding nut 94 is at one endof the slot 92 or the other. Sleeve 98 slidably engages with outersurface 100 of the control arm-mounting portion 90. A bearing 102 isprovided to facilitate pivotal engagement with the stabilizer brackets88 a, 88 b (see FIG. 5). Retaining ring 104 holds the bearing 102 inopening 106 on the control arm-mounting portion 90.

[0050] Rocker arm mounting portion 108 also includes a bearing 110 tofacilitate pivotal engagement with the rocker arm 76. Distal end of theshaft 112 includes a sleeve 114 and a spring cap 116 rigidly mountedthereto. Surface 118 of the spring cap 116 engages with surface 120 ofspring 122. The opposite surface 124 of the spring 122 engages withsurface 126 of the sleeve 98.

[0051] Stabilizer preload adjustment screw 128 is provided in thecontrol arm-mounting portion 90 for sliding the sleeve 98 towards thespring 122. As will be discussed in detail below, the preload adjustmentscrew 128 permits the spring 122 to be preloaded to a desired levelwithin the stabilizer member assemblies 84 a, 84 b.

[0052]FIG. 4A illustrates a double-acting spring assembly suitable foruse as an alternate stabilizer member assembly 410 in accordance withthe present invention. Control arm mounting portion 412 is attached to asliding rod 414 that extends through a fixed divider 416 that isattached to a housing 418. A sliding retainer 420 that slides within thehousing 418 is attached to the other end of the rod 414. A first spring422 wraps around the rod 414 and is interposed between the slidingretainer 420 and the fixed divider 416. A second spring 424 wrap aroundthe rod 414 and is interposed between the fixed divider 416 and anadjustable spring cap 426. The rod 414 has a threaded portion 428 thatpermits the location of the spring cap 426 to be adjusted so that apreload can be applied to the springs 424, 426. The housing 418 includesa rocker arm mounting portion 430. The stabilizer member assembly 410tops-out or bottoms-out when either of the springs 422, 424 are fullycompressed. In one embodiment, the alternate stabilizer member assembly410 is substituted for one of the stabilizer member assemblies 84 a, 84b, and a rigid rod is substituted for the other stabilizer membersassembly.

[0053] FIGS. 5-7 illustrate various views of the stabilizer assembly 74with the primary support structure 22 removed. In a horizontal restingstate, the shock absorbers/spring assemblies 70 a, 70 b (see FIG. 8)provide a downwardly biasing force 140 a, 140 b on the spindle housings36 a, 36 b. The horizontal resting state refers to the snowmobile beingstationary on a substantially horizontal surface. When an upward bumpforce 144 greater than the force 140 a is imposed on the spindle housing36 a, the lower control arm 32 a will rotate in a direction 146 a aroundthe lower control arm axis 34 a. Rotation of the lower control arm 32 adisplaces the stabilizer bracket 88 a in a direction 148. Assuming thatthe stabilizer member assembly 84 b is at its fully elongated ortopped-out position, displacement of the stabilizer bracket 88 a in thedirection 148 will have the effect of rotating the rocker arm 76 in thedirection 142, which in turn will move the stabilizer member assembly 84b in a direction 150.

[0054] Once the stabilizer member assembly 84 b is in the fullyelongated position, movement of the stabilizer bracket 88 b in thedirection 150 will have the effect of raising the lower control arm 32 bin opposition to the force 140 b provided by the shock absorber 70 b.Consequently, spring force from the shock absorber 70 b will betransferred to the lower control arm 32 a on the other side of themodular front suspension system 20.

[0055] In another embodiment, preload adjustment screws 128 a, 128 b areadvanced so that the sleeves 98 a, 98 b partially compress the springs122 a, 122 b. When in the horizontal resting state, any load on thesprings 122 a, 122 b will cause the stabilizer member assemblies 84 a,84 b to elongate to their maximum length and rotate the rocker arm 76 ina direction 142. Ultimately, the stabilizer member assemblies 84 a, 84 bare in their fully extended state and do not rotate the rocker arm 76any further. At this point, further advancing the sleeves 98 a, 98 busing the preload adjustment screws 128 a, 128 b will develop a preloadin the springs 122 a, 122 b.

[0056] When the bump force 144 increases to a level that is greater thanthe shock absorber/spring assembly force 140 a, the lower control arm 32a rotates in a direction 146 a. Rotation in the direction 146 a isinitially resisted by a combination of the downward force 140 b on thespindle housing 36 b, as discuss above, and the spring force from spring122 a. As the spring 122 a is compressed, the spring force of spring 122a rises until it overcomes the downward force 140 b from the shockabsorber/spring assembly 70 b, forcing the lower control arm 32 b torotate in the direction 146 b. As the lower control arm 32 b rotates inthe direction 146 b, the shock absorber/spring assembly 70 b iscompressed and the force 140 b increases. A component of the increasedforce 140 b is transmitted through the stabilizer assembly 74 to thespindle housing 36 a.

[0057] The configuration discussed above allows for a non-linearrelationship between the stabilizer mechanism 74 and the shockabsorber/spring assemblies 70 a, 70 b. For example, it is possible tohave a firm initial roll stiffness of the snowmobile for smooth cornersand soft roll stiffness for bumpy corners by increasing the preload onthe springs 122 a, 122 b. Alternatively, for a more linear relationshipbetween the stabilizer mechanism 74 and the shock absorber/springassemblies 70 a, 70 b, less preload on the springs 122 a, 122 b is used.

[0058] One practical application of the present stabilizer assembly 74is that is provides initially very stiff displacement of the lowercontrol arms 32 a, 32 b for smooth covering on relatively smoothsurfaces. When rough terrain is encountered, further displacement of thelower control arms 32 a, 32 b will require less additional force thanthe original displacement. In one embodiment, the force-displacementcurve for the present stabilizer assembly 74 is essentially a stepfunction in which the force per unit displacement is reduced after aninitial amount of displacement is achieved.

[0059]FIGS. 8 and 9 illustrate a modular front suspension system 20 inaccordance with the present invention mounted to a snowmobile frame 200.The primary support structure 22 is attached to upper frame members 202a, 202 b at upper frame mounting locations 204 a, 204 b. Lower framemembers 206 a, 206 b are attached to the primary support structure 22 atlower frame mounting locations 208 a, 208 b. Removable fasteners, suchas bolt, are preferred for attaching the primary support structure 22 tothe snowmobile frame 200. The primary support structure 22 permits easyassembly and removal of the modular front suspension system 20 from thesnowmobile frame 200. Additionally, the primary support structure 22provides a substantial barrier that protects motor compartment 210.

[0060] The snowmobile frame 200 includes a left frame portion 220 a anda right frame portion 220 b. The left and right frame portions 220 a,220 b are join together by an upper cross piece 224 and a lower crosspiece 226 immediately behind the engine compartment 210. Verticalsupports 209 a, 209 b extends between frame members 202 a, 206 a and 202b, 206 b, respectively. The lower frame members 206 a, 206 b extendrearward of the engine compartment 210. Upper rear frame member 228 aextends from the upper portion of the vertical support 209 a to thedistal rearward end of the lower frame member 206 a. The frame members228 a and 206 a are joined at a mounting plate 232 a. Upper rear framemember 228 b extends from about the upper portion of the verticalsupport 209 b to the distal rearward end of the lower frame member 206b. The frame members 228 b and 206 b are joined at a mounting plate 232b. The rearward frame members 228 a, 206 a are not connected to therearward frame members 228 b, 206 b at any location behind the verticalsupports 209 a, 209 b and the cross pieces 224, 226, thereby reducingthe weight of the frame 200. The independent, free-floating nature ofthe rearward frame members 228 a, 206 a and 228 b, 206 b is believed toimprove the handling properties of the snowmobile.

[0061]FIG. 9 is a side view of the snowmobile chassis 240 including aprotective shell 214 attached to, and extends between, the rearwardframe members 228 a, 206 a and 228 b, 206 b. The protective shell 214prevents snow and debris from reaching seat region 402. In theillustrated embodiment, the protective shell 214 is constructed from aresin-based material, such as fiberglass or fiberglass reinforced withKevlar® fibers or other lightweight reinforcing materials. Kevlar is anaromatic polyamide fiber of extremely high tensile strength and greaterresistance to elongation than steel. It has high-energy absorptionproperties that make it particularly suitable for use as a reinforcingmaterial for plastic composites.

[0062] The protective shell 214 is typically not a structural member fortransferring loads between the rearward frame members 228 a, 206 a and228 b, 206 b. Loads are transferred between these rearward frame membersby the rear suspensions system for the endless track, such as thesuspension systems disclosed in U.S. Pat. Nos. 5,370,198 and 5,667,031,and U.S. patent application Ser. No. 08/853,442 entitled VehicleSuspension System with Variable Geometry, filed May 9, 1997.

[0063] The primary support structure 22 with the front suspensioncomponents removed is shown mounted to the snowmobile chassis 240.Center opening 72 is typically perpendicular to the longitudinal axis ofthe snowmobile frame 200. Steering brackets 24 are located behind theprimary support structure 22 in the motor compartment 210 to protectthem from damage during impacts with obstacles. Additionally, heatgenerated within the motor compartment 210 may reduce the accumulationof ice and snow on the steering linkage mechanism (not shown).

[0064]FIGS. 10, 11, and 12 are various perspective views of a snowmobilechassis 240 of the present invention. The protective shell 214 has acenter portion 251 and left and right side portions 250, 252 extendingdownward towards the upper rear frame members 228 a, 228 b,respectively. The protective shell 214 can flex at the intersection ofthe side portions 250, 252 and the center portion 251 during snowmobileoperation. Running boards 254, 256 extend laterally outward from theside portions 250, 252, respectively.

[0065] As best seen in FIG. 12, the protective shell 214 defines a topedge of an endless belt channel 260 extending along the rear portion ofthe chassis 240 between the rear frame members 206 a, 228 a and 206 b,228 b. Drive shaft 262 extends across the width of the endless beltchannel 260 for engagement with the endless belt (see FIG. 14). In theillustrated embodiment, one end of the drive shaft 260 is directlymechanically coupled to a gearbox 264. The gearbox 264 has a drivenpulley input opening 266 for receiving a driven pulley 286 (see FIG.14). A rotor 270 and a caliber 272 are located on the other end of thedrive shaft 262 for providing a breaking force. The rotor 270 andcaliber 272 operate as a conventional disk brake system.

[0066]FIGS. 13 and 14 illustrate a side and top view of a snowmobilechassis 240 and drive train in accordance with the present invention.Motor 280 is retained in the motor compartment 210 by various motormounts 282, 284. In the illustrated embodiment, motor mounts 282 arerigidly connected to the primary support structure 22. In theillustrated embodiment, the motor 280 is a 700 cc twin cylinder, liquidcooled engine generating about 120-125 HP at 8150 RPM, with 83 footpounds of torque at 8000 RPM, available from Polaris Industries, Inc. ofRoseau Minn. The motor 280 is arranged with carburetors 287 locatedtowards the front, immediately behind the primary support structure 22.Exhaust ports 288 are located on opposite sides of the motor 280.

[0067] As is often the case, the exhaust ports 288 are located higher onthe motor 280 than the carburetor 287. By arranging the motor 280 withthe exhaust ports 288 towards the rear, there is more room to lower themotor 280 further into the chassis 240, resulting in a lower center ofgravity for the snowmobile 400. In the embodiment illustrated in FIG.13, the locations of the carburetors 287 and exhaust ports 288 generallyfollow the contour or slope of the upper frame members 202 a, 202 b. Itis estimated that the motor 280 is located about 5.1 centimeters toabout ⁻0.6 centimeters (2 to 3 inches) lower in the chassis 240 than oncomparably powered snowmobiles.

[0068] The carburetors 287 tend to require more space than the exhaustsystem 290. Consequently, locating the carburetors 287 in the frontallows the motor 280 to be located closer to the rear of the motorcompartment 210. Locating the exhaust system 290 between the motor 280and the steering column 292 contributes to mass centralization, alowering the center of gravity and reducing the overall length of thesnowmobile, thereby increasing handling performance and ride quality.Additionally, locating the carburetors 287 on the front of the motor 280is believed to reduce the occurrences of vapor lock. Finally, when thesnowmobile is parked in a slightly downhill configuration, fuel willdrain from the motor 280 towards the carburetor 287, reducing the chanceof engine flooding.

[0069] Drive clutch 300 is coupled directly to the crankshaft 302 of themotor 280. The drive clutch 300 is mechanically coupled to the drivenpulley 286 by a continuous belt 304. As discussed above, the drivenpulley 286 is directly mechanically coupled to the gear box 264. Poweris transmitted through a matched set of gears, thereby eliminating theintermediate chain drive that typically is located between the drivepulley and the drive shaft. This partial direct drive configurationincreases reliability of power transmission to the track or belt. Thedrive shift 262 includes a series of drive wheels 340 havingappropriately spaced teeth 342 that engage with ridges on the endlesstrack or belt. A suitable endless track or belt is available fromCamoplast Thermoplastic Group of Sherbrooke, Quebec.

[0070] An oil tank 350 is located under the steering column 292. A fueltank 352 is located on the protected shell 214 behind the fuel tank 352.A steering column support structure 354 extends over the fuel tank 352and supports the steering column 292. A flap 356 is mounted on the endof the protective shell 214 to reduce the snow and debris thrown by theendless track.

[0071] As best seen in FIG. 14, a torque arm 310 extends between abracket 312 rigidly attached to the frame 200 and the driven pulley 268.The torque arm 310 provides a counteracting force 314 that opposes theforce 316 generated by the drive belt 304. A quick release pin 318 isprovided on the torque arm 310 to permit the drive belt 304 to be easilyreplaced as needed. As best illustrated in FIG. 15, the torque arm 310includes a bearing 320 that engages with a distal end of the drivenpulley 268.

[0072]FIG. 16 is an exploded view of the gear box 264 in accordance withthe present invention. Since the motor 280 is mounted with the crankshaft 302 facing to the right, the drive clutch 300 is turned in theopposite direction of rotation than on a conventional snowmobile. Thegear box 264 reverses the direction of the drive system rotation fordelivery to the drive shaft 262 and provides the final ratio reductionfor the drive train. The driven pulley 286 is directly coupled to afirst gear 330 through the opening 266. The gear 330 preferably includesbearings 332 to minimize internal friction and wear. The first gear 330is meshed with second gear 334, which reverses the direction of rotationof the drive system. The drive shaft 262 is directly coupled to thesecond gear 334 through The opening 336. In the illustrated embodiment,the gears 330, 334 are covered in a housing 338 with appropriatemounting holes for attachment to the vehicle chassis 240.

[0073] The complete disclosures of all patents, patent applications, andpublications are incorporated herein by reference as if individuallyincorporated. Various modifications and alterations of this inventionwill become apparent to those skilled in the art without departing fromthe scope and spirit of this invention, and it should be understood thatthis invention is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A modular front suspension system for asnowmobile having a chassis with a powered endless belt drive system anda pair of forwardly mounted steerable skis attached to the chassis bythe modular front suspension system, the modular front suspension systemcomprising: a primary support structure having first and second ends, acenter opening and at least one mounting surface attachable to thechassis; a pair of upper control arms pivotally connected to the firstand second ends of the primary support structure at upper control armaxes, respectively; a pair of lower control arms pivotally connected tothe first and second ends of the primary support structure at lowercontrol arm axes, respectively; a pair of ski spindle housings pivotallyconnected to distal ends of the upper and lower control arms,respectively, the ski spindle housings being connectable to thesteerable skis; and a stabilizer assembly mechanically coupling the skispindle housings.
 2. The system of claim 1 wherein the stabilizerassembly extends through the center opening.
 3. The system of claim 1further comprising: a pair of shock mounts pivotally attached to one ofthe upper control arm, primary support structure or the vehicle chassis;and a pair of shock absorber attached to the shock mounts and thespindle housings, respectively.
 4. The system of claim 3 furthercomprising a link pivotally connecting the shock mounts and therespective lower control arms.
 5. The system of claim 1 furthercomprising: a pair of shock mounts pivotally attached to the primarysupport structure; a link connecting the pair of shock mounts to therespective lower control arms; and a pair of shock absorber connected tothe shock mounts and the spindle housings, respectively.
 6. The systemof claim 1 wherein the primary support structure further comprisessteering brackets for receiving a steering linkage connectable to thesteerable skis.
 7. The system of claim 1 wherein the primary supportstructure further comprises motor mounting locations.
 8. The system ofclaim 1 wherein the stabilizer assembly is connected to one of the lowercontrol arms, the upper control arms, the shock mounts or the lowershock mounts.
 9. The system of claim 1 wherein the stabilizer assemblycomprises: first and second stabilizer brackets attached to the lowercontrol arms, respectively; a rocker arm having first and second endspivotally mounted on the primary support structure; a first stabilizermember assembly pivotally connected to the first stabilizer bracket andthe first end of the rocker arm; and a second stabilizer member assemblypivotally connected to the second stabilizer bracket and the second endof the rocker arm.
 10. The system of claim 9 wherein the firststabilizer member assembly comprises: an extendable rod assembly havinga maximum extension and a spring cap fixed thereto; a sleeve slidablyengaged with the extendable rod assembly adjacent to the firststabilizer bracket; and a spring arranged around the extendable rodassembly and interposed between the spring cap and the sleeve.
 11. Thesystem of claim 10 further comprising an adjustment mechanism forsliding the sleeve along the extendable rod assembly to apply a bias ofthe spring when the extendable rod as at the maximum extension.
 12. Thesystem of claim 10 wherein the extendable rod assembly comprises atelescoping structure.
 13. The system of claim 9 wherein the secondstabilizer member assembly comprises: an extendable rod assembly havinga maximum extension and a spring cap fixed thereto; a sleeve slidablyengaged with the extendable rod assembly adjacent to the secondstabilizer bracket; and a spring arranged around the extendable rodassembly and interposed between the spring cap and the sleeve.
 14. Thesystem of claim 13 wherein the first and second stabilizer memberassemblies are in a fully extended configuration when the snowmobile isin a substantially horizontal resting state.
 15. The system of claim 9wherein the first stabilizer member assembly comprises a double-actingspring assembly and the second stabilizer members assembly comprises arigid shaft.
 16. The system of claim 9 wherein the rocker arm is locatedin the center opening of the primary support structure.
 17. The systemof claim 1 wherein the primary support structure comprises one of anextrusion, a casting, a welded structure or a formed structure.
 18. Thesystem of claim 1 wherein the respective upper control arm axes arelocated above the lower control arm axes when the primary supportstructure is attached to the chassis.
 19. A modular front suspensionsystem for a snowmobile having a chassis with a powered endless beltdrive system and a pair of forwardly mounted steerable skis attached tothe chassis by the modular front suspension system, the modular frontsuspension system comprising: a primary support structure comprising ahollow member having first and second ends, a center opening and atleast one mounting surface attachable to the chassis; a pair of uppercontrol arms pivotally connected to the first and second ends of theprimary support structure at upper control arm axes, respectively; apair of lower control arms pivotally connected to the first and secondends of the primary support structure at lower control arm axes,respectively; a pair of ski spindle housings pivotally connected todistal ends of the upper and lower control arms, respectively, the skispindle housings being connectable to the steerable skis; a pair ofshock mounts pivotally attached to one of the upper control arm orprimary support structure, respectively; and a pair of shock absorberattached to the shock mounts and the spindle housings, respectively. 20.A stabilizer assembly for a front suspension system of a snowmobile, thefront suspension system having a pair of control arms pivotallyconnected to the snowmobile, a pair of skis pivotally connected todistal ends of the control arms, and biasing members biasing the pair ofcontrol arms downward relative to the snowmobile, the stabilizerassembly comprising: first and second stabilizer brackets attached tothe control arms, respectively; a rocker arm having first and secondends pivotally mounted to the snowmobile; a first stabilizer memberassembly pivotally connected to the first stabilizer bracket and thefirst end of the rocker arm; and a second stabilizer member assemblypivotally connected to the second stabilizer bracket and the second endof the rocker arm.
 21. The assembly of claim 20 wherein the firststabilizer member assembly comprises: an expendable rod assembly havinga maximum extension and a spring cap fixed thereto; a sleeve slidablyengaged with the extendable rod assembly adjacent to the firststabilizer bracket; and a spring arranged around the extendable rodassembly and interposed between the spring cap and the sleeve.
 22. Theassembly of claim 21 further comprising an adjustment mechanism forsliding the sleeve along the extendable rod assembly to apply a bias ofthe spring when the extendable rod is as the maximum extension.
 23. Theassembly of claim 21 wherein the extendable rod assembly comprises atelescoping structure.
 24. The assembly of claim 20 wherein the secondstabilizer member assembly comprises: an extendable rod assembly havinga maximum extension and a spring cap fixed thereto; a sleeve slidablyengaged with the extendable rod assembly adjacent to the secondstabilizer bracket; and a spring arranged around the extendable rodassembly and interposed between the spring cap and the sleeve.
 25. Theassembly of claim 20 wherein the first and second stabilizer memberassemblies are in a fully extended configuration in a substantiallyhorizontal resting state.
 26. A stabilizer assembly for a frontsuspension system of a vehicle, the front suspension system having apair of control arms pivotally connected to the vehicle, a pair ofwheels pivotally connected to distal ends of the control arms, andbiasing members biasing the pair of control arms downward relative tothe vehicle, the stabilizer assembly comprising: first and secondstabilizer brackets attached to the control arms, respectively; a rockerarm having first and second ends pivotally mounted to the vehicle; afirst stabilizer member assembly pivotally connected to the firststabilizer bracket and the first end of the rocker arm; and a secondstabilizer member assembly pivotally connected to the second stabilizerbracket and the second end of the rocker arm.
 27. A stabilizer assemblyfor a front suspension system of a snowmobile, the front suspensionsystem having a pair of control arms pivotally connected to thesnowmobile, a pair of skis pivotally connected to distal ends of thecontrol arms, and biasing members biasing the pair of control armsdownward relative to the snowmobile, the stabilizer assembly comprising:first and second stabilizer brackets attached to the control arms,respectively; a rocker arm having first and second ends pivotallymounted to the snowmobile; a first stabilizer member assembly pivotallyconnected to the first stabilizer bracket and the first end of therocker arm, the first stabilizer member assembly comprising anextendable rod assembly having a maximum extension and a spring capfixed thereto, a sleeve slidably engaged with the extendable rodassembly adjacent to the first stabilizer bracket, and a spring arrangedaround the extendable rod assembly and interposed between the spring capand the sleeve; and a second stabilizer member assembly pivotallyconnected to the second stabilizer bracket and the second end of therocker arm; the second stabilizer member assembly comprising anextendable rod assembly having a maximum extension and a spring capfixed thereto, a sleeve slidably engaged with the extendable rodassembly adjacent to the second stabilizer bracket, and a springarranged around the extendable rod assembly and interposed between thespring cap and the sleeve.
 28. The assembly of claim 27 wherein thefirst and second stabilizer member assemblies are in a fully extendedconfiguration in a substantially horizontal resting state.
 29. Theassembly of claim 27 wherein springs of the first and second stabilizermember assemblies comprise a preload in the horizontal resting state.30. The assembly of claim 25 wherein initial upward displacement of oneof the skis is resisted by a first force, and subsequent upwarddisplacement of that ski is resisted by a second force proportionallyless than the first force.
 31. The assembly of claim 25 wherein initialupward displacement of one of the skis is resisted by a first force, andsubsequent upward displacement of that ski is resisted by a second forceproportional to the first force.
 32. A chassis for a snowmobile havingan endless belt drive system, the chassis comprising: a plurality offront structural members defining a motor compartment; front suspensionsystem mounting locations on distal ends of two or more of the frontstructural members; a pair of independent, rear structural membersrigidly connected to the front structural members and extendingrearwvardly from the motor compartment on opposite sides of an endlessbelt channel; and a protective shell extending between the pair of rearstructural members and over the endless belt channel, the protectiveshell comprising a light-weight, resin based material transferringsubstantially no loads between the pair of rear structural members. 33.The snowmobile chassis of claim 32 further comprising a rear suspensionsystem extending between the pair of rear structural members, the rearsuspension system transferring substantially all loads between the pairof rear structural members.
 34. The snowmobile chassis of claim 33further comprising a motor located in the motor compartment, the motorhaving at least one carburetor positioned on a first side of the motoradjacent to the front suspension system mounting locations and at leastone exhaust port positioned on an opposite side of the motor andgenerally in the direction of the rear structural members.
 35. Asnowmobile assembly having an endless belt drive system comprising: asnowmobile chassis having a motor compartment at a front portion and anendless belt channel at a rear portion; a motor located in the motorcompartment, the motor having at least one exhaust port positionedtoward the rear portion of the snowmobile chassis; a drive clutch on themotor; a driven pulley on the gear box located adjacent to the endlessbelt channel, an endless belt drive shaft located in the endless beltchannel and mechanically coupled directly to the gear box; a drive beltmechanically coupling the drive clutch to the driven pulley; and atorque arm connecting the driven pulley to the snowmobile chassis. 36.The snowmobile of claim 35 wherein the gear box comprises two or moregears directly coupling the driven pulley to the endless belt driveshaft.